Photo-electrical transducer

ABSTRACT

A photo-electrical transducer element comprising a semiconductor body, a rectifying barrier formed in the semiconductor body, and electrodes formed on said semiconductor body on both sides of said barrier. A deep-level-forming impurity is heavily doped in the neighborhood of the rectifying barrier.

0 United States Patent 1 1 1111 3,928,865

Yamashita 5] Dec. 23, 1975 [54] PHOTO-ELECTRICAL TRANSDUCER 3,390,311 6/1968 Aven 317/237 i 3,417,248 12/1968 Hall 250/211 [75] Inventor m Ikeda Japan 3,424,910 1/1969 Mayer 250/211 [73] A i M t hi El t i I d i l C 3,436,613 4/1969 Gerhard 317/234 Ltd Kadoma Japan 3,461,356 8/1969 Yamash1ta 317/234 [22] Filed: Apr. 21, 1971 Primary Examiner-Martin H. Edlow [21] Appl 136l59 Attorney, Agent, or FirmStevens, Davis, Miller &

Mosher [30] Foreign Application Priority Data .Apr. 24, 1970 Japan 45-35757 [57] ABSTRACT [52] US. C1.2 357/30; 357/15; 357/64 A photo electrical transducer element comprising a [51] Int. Cl. ..H01L 29/48; H01L 29/56; Semiconductor body, a tif i barrier f d i h HOIL 29/167 semiconductor body, and electrodes formed on said Field of Search" 317/235 235 235 AQ semiconductor body on both sides of said barrier. A deep-level-forming impurity is. heavily doped in the References C'ted neighborhood of the rectifying barrier.

UNITED STATES PATENTS 3,271,637 9/1966 Webb 317/234 1 Claim, 3 Drawing Figures JJIII 1 r I I IIIIIIIIIIIIIIIIII PHOTO-ELECTRICAL TRANSDUCER This invention relates to a photo-electrical transducer.

Conventionally, as photo-electrical transducers, there have been developed photoconductive cells and solar (photovoltaic) cells using semiconductors.

However, they have a disadvantage in that their eff ciency cannot be made very high. For example, a solar cell using silicon has an efficiency of about 24% and one using gallium arsenide has an efiiciency of about 28%. Thus for utilizing conventional elements as a power source, a considerable number of solar cells must be used.

An object of this invention is to provide a photo-electrical transducer having a high efficiency.

According to this invention, there is provided a photoelectrical transducer comprising a semiconductor body including a rectifying barrier and doped with a deep-levelforming impurity in the neighborhood of said rectifying barrier, and electrodes provided on said semiconductor body on both sides of said rectifying barrier, said transducer having an efficiency much better than the conventional one.

Now, description will be made with reference to the accompanying drawing, in which:

FIG. 1 is a cross'section of a conventional solar cell;

FIG. 2 is a cross-section of an embodiment of a photoelectrical transducer according to this invention; and

FIG. 3 is a crosssection of another embodiment of a photo-electrical transducer.

First, as an example of photo-electrical transducers, a conventional solar cell will be described. Referring to FIG. 1, in which silicon is used as the matrix semiconductor, reference numerals l and 2 indicate p and n type silicon, 3 a pn junction, 4 and 5 upper and lower electrodes, respectively. A light beam is arranged to radiate from the upper side. When photons having energies of not less than the forbidden band width of the semiconductor impinge thereon, electrons in the valence band may be excited to the conduction band and an electromotive force is generated.

The efficiency is defined by the ratio of output to input energy and usually is 20 to 30%.

In this specification, a rectifying barrier means a pn junction, metalsemiconductor junction, etc. Further, a deep-level-forming impurity means an impurity which forms a deep energy level or levels in the forbidden band and has a greater probability for recombination than that for trapping free carriers, such as iron, copper, gold, manganese and nickel.

An embodiment of this invention will now be described. FIG. 2 shows a metal-semiconductor junction using p type silicon. Reference numeral 6 indicates a p type silicon, 7 a metal electrode using niobium, 8 a metal-semiconductor junction, 9 a region heavily doped with a deep-level-forming impurity, 10 a metal electrode. The element shown in FIG. 2 may be made as follows. First a pellet of p type silicon single crystal is oxidized in an oxidizing atmosphere to form a silicon oxide film on the surface. Then, the silicon oxide film on one side is removed by an etching technique and a deep-level-forming impurity, in this case copper, is vapor deposited on the exposed surface. Then, the pellet is heated in an inert atmosphere to diffuse the impurity. Copper impurities diffuse through the silicon body and these are mostly trapped in the neighborhood of the opposite silicon oxide-silicon interface to form the region 9 of FIG. 2. Then, the silicon oxide film is removed, and as the electrode on the light receiving side niobium is thinly sputtered and as the electrode on the other side gold or gallium is alloyed. The samples thus made but with varying diffusion conditions developed the following open circuit voltages under constant illumination, at a wavelength of 1000 mu:

Table l Sample number Copper diffusion Open circuit voltage I no diffusion 0.30 mV 2 800C 60 min. 0.95 mV 3 I000C l0 min. 2.6 mV 4 I000C 30 min. 2.6 mV 5 I000C I min. 6.5 mV

As is evident from the table, copper diffusion increases the efficiency of photoelectric transformation.

Table 2 Sample number Copper diffusion Open circuit voltage I no diffusion 4.0 mV 2 800C 60 min. I l mV 3 [000C l0 min. 35 mV 4 I000C 30 min. 34 mV 5 |000C I80 min. I20 mV In this case also, copper diffusion increases the photoelectrical transducing efficiency.

In the foregoing, silicon is employed as the semiconductor, but it may be substituted by any one of GaAs, CdTe, Ge, InP, AlSb, GaP, CdS, etc.

As is apparent from the foregoing description, a photoelectrical transducer according to this invention has a higher efficiency than a conventional one and hence provides a larger current with a smaller area. Thus, smaller and lighter elements can be provided,

What is claimed is:

l. A photoelectric transducer comprising a semiconductor wafer, a metal layer on the semiconductor wafer, the semiconductor wafer and the metal layer forming a Schottky barrier therebetween, and a region in the neighborhood of the Schottky barrier heavily doped with a deep-level impurity selected from the group consisting of copper, gold, iron, nickel and manganese. 

1. A PHOTOELECTRIC TRANSDUCER COMPRISING A SEMICONDUCTOR WAFER, A METAL LAYER ON THE SEMICONDUCTOR WAFER, THE SEMICONDUCTOR WAFER AND THE METAL LAYER FORMING A SCHOTTKY BARRIER THEREBETWEEN, AND A REGION IN THE NEIGHBORHOOD OF THE SCHOTTKY BARRIER HEAVILY DOPED WITH A DEEP-LEVEL IMPURITY SELECTED FROM THE GROUP CONSISTING OF COPPER, GOLD, IRON, NICKEL AND MANGANESE. 